This invention relates to the blending of particulated food products, and more particularly to a method of blending such products using agitators mounted on elongated, horizontal rotatable shafts.
Blending machines having one or more horizontal agitator shafts positioned in an elongated tub are in common use in the blending of particulated food products such as different mixtures of diced or ground meat, poultry, vegetables, sauces and the like. The most commonly used machine is a twin shaft blending machine, wherein two horizontal agitator shafts are mounted in a tub parallel to each other. The agitators mounted on the shafts come in many designs, with the most common being a ribbon agitator wherein a spiral ribbon of steel is mounted on each shaft by spokes extending radially from the shafts.
As the agitator shafts rotate, the spiral ribbons push through the product causing it to move in a rotating column with the agitator, and, because the ribbons are spiral, to move slowly in a direction parallel to the agitator shafts, i.e. from end-to-end in the tub. Typically, the agitators are rotated in opposite directions so that the product is moved in opposite end-to-end directions in the tub by each agitator, with the product being continuously folded into the center of the tub by each counter-rotating agitator so that the two rotating columns mix with each other.
After the blending has been carried on sufficiently to mix the product to a desired degree, one of the agitator shafts is reversed in direction of rotation. This causes both agitators to urge the product towards the discharge end of the tub and out through the discharge doors at that end of the tub.
An example of such a blending machine is that shown in U.S. Pat. No. 4,733,607, issued Mar. 29, 1988 to Leonard J. Star and Jesse J. Tapscott. In this patent, the apparatus also includes a steam jacket surrounding the blending tub so that the product can be cooked as the agitators mix and blend the product together. Also, in the patent the spiral ribbons have scrapers mounted thereon for scraping the trough walls to keep the product from sticking on the hot cooking surfaces. Ribbon blender machines used for cold blending will not have a steam jacket, nor will the scrapers shown in the above patent be required.
These blenders are used for batch operations, wherein the particulated ingredients are loaded into the tub, generally to a level just above the top of the spiral ribbon, and the agitator shafts are then driven.
The ribbon agitators may be made in different shapes. For example, instead of being in a flat rectangular shape, as in the above mentioned U.S. Pat. No. 4,733,607, the ribbons may be round or tubular in cross-section. The ribbons may also be non-continuous and made of several short sections along the length of the agitator shafts. For some products, paddles of different shapes are attached to the agitator shaft in place of the ribbons, the paddles being oriented to have their faces inclined to the axes of rotation. Sometimes, the agitator may be made up a combination of ribbons and paddles. Regardless of the specific designs, the action will be the same, i.e. the agitators will cause the product in contact therewith to move towards the center of the tub for blending and also lengthwise of the tub.
Ribbon agitators have also been used in continuous blenders, i.e. blenders in which the ingredients are continually added at one end of the blender and with the blended product being continuously removed from the other end of the blender. Such continuous blenders have a substantially elongated tub or trough and a horizontal shaft extending the length of the tub. The shaft has inner and outer spiral ribbons along the length thereof, of the shaft. One of the ribbons being wound as a right hand spiral while the other ribbon is wound as a left hand spiral. Thus when the shaft is rotated, the outer ribbon will urge the product towards the discharge end of the tub while the inner ribbon urges the product in the opposite direction towards the inlet end of the tub. This counter movement provides the blending of the product as the total product moves gradually as a whole towards the discharge end.
Continuous blenders currently in use are successful only if the separate ingredients are fed into the blender in exactly the right proportion and continuously. Such continual metering of the ingredients is difficult and few plants are set up for this. Further, this system will work only on products that are very easy to mix, such as fruit or salad mixes without sticky dressings. Because of these limitations, few continuous blenders are in use.
The twin horizontal shaft batch blenders also have their limitations. The most significant problem is the amount of mechanical damage that the agitators cause to the product as it is blended. To provide a pack with high quality appearance, the different ingredients must be uniformly blended together with a minimum amount of mechanical breakdown of any one of the ingredients. If the product is a sauce-based blend of particles, such as stew, the objective is to keep the particles of meat and vegetables in suspension during blending and with minimum damage to the softer vegetable ingredients of the stew. If the product is also cooked as it is being blended, many of the ingredients will become very fragile as they get closer to being fully cooked and will break down very easily. When ground beef is cooked, as for example for taco meat, it is desirable to end up with an evenly cooked product with natural looking, irregular sized chunks of meat. When cooked in a jacketed blender with a conventional agitator system, the meat is broken into universally small particles and has an unnatural mealy look when cooked.